Materials formed by refractory grains bound in a matrix of aluminum nitride or sialon containing titanium nitride

ABSTRACT

The invention relates to refractory materials that may be used in iron and steel metallurgy comprising, in % by weight: 
     A! 32 to 87% of particles and/or grains of at least one refractory material, the melting temperature and thermal dissociation temperature of which are greater than 1700° C.; 
     B! 7 to 50% of an in situ-formed binding matrix and consisting of a sialon, AIN or one of its polytypes, or a mixture thereof; 
     C! 2 to 40% of a material based on titanium nitride TiN dispersed in the matrix; and, optionally, 
     D! 0 to 42% of hexagonal boron nitride, amorphous carbon and/or crystallized graphite dispersed in the binding matrix.

The invention relates to novel refractory materials consisting of grainsbound in a matrix of aluminium nitride or of sialon, containing titaniumnitride and, optionally, particles of graphite and/or boron nitridewhich are dispersed within it, as well as to a process for manufacturingthem.

There is a need in iron and steel metallurgy, as well as in aluminiummetallurgy, for refractory materials of increasing performance andreliability: what is required in fact is to improve, simultaneously, thecorrosion resistance, the hot strength and the heat shock resistance.

The main applications in question are:

refractory ceramic components used in devices for shrouding orregulating the feed streams of cast iron or steel. Particular examplesof such components are slide-valve shut-off plates, feed-stream shroudtubes, submerged nozzles and stopper rods;

refractory ceramic components used in agitation devices, either of themechanical or gas-injection kind, in the molten metal;

seating blocks serving as a housing and support for gas-injectiondevices and for devices for regulating metal feed streams, as well asimpact tiles for ladles and tundishes;

internal lining of blast furnaces and, in particular, of the boshes,twyer belt and crucible;

founding accessories, for cast iron, steel and special alloys, such asnozzles, bots and flow-offs.

The wide variety of stresses which these materials experience oftenresults from the equipment being operated in a non-continuous manner:there is the heat shock at start-up and then at the end of a cycle, andduring a cycle the refractory components come successfully into contactwith molten metal and then molten slag. Finally, between two cycles, therefractory components remaining at a relatively high temperature aresubjected to oxidation by the ambient air.

Purely mechanical stresses are always present: thermal shocks andstresses resulting from handling operations, confinement stressescreated by a metallic outer jacket and, finally, in the case ofstream-regulating systems, stresses associated with the actual functionof the refractory components, that is to say shut-off effects andmovements.

Finally, it will be noted that in all cases the refractory components inquestion are subjected to the erosive action of molten metal.

The list of properties desired for these refractory materials thereforecomprises the following:

high hot strength in order to withstand either mechanical stresses orthe effects of erosion by the flow of metal or slag;

excellent resistance to chemical corrosion by cast irons, steels andspecial alloys;

good resistance to corrosion by iron- and steel-making slags and coverpowders;

properties of not being wetted by the metals, slags and cover powders soas to limit the extent to which they infiltrate into grain boundaries,cracks and pores, but also to reduce the risks of the skins catching asthe product cools down;

good resistance to atmospheric oxidation;

excellent heat shock resistance;

the property of not being oxidized by aluminium and by calcium dissolvedin some steels;

tribological properties for moving components.

Despite a complex and corrosive environment, the refractory componentsin question need to be very reliable since any accidental failure mayhave catastrophic consequences, both for the plant and for theoperators.

Materials based on a silicon carbide granulate, bound in a sialonmatrix, are widely used as bricks for lining blast furnaces. In thisapplication the material is intended to withstand a continuous flow overits surface of cast iron for more than 10 or 15 years. However, sialonis slightly soluble in iron and therefore a binding matrix has beensought which is more inert with respect to the metal.

Refractory materials are known from EP-A-0,480,831 which are formed byan alumina-based granulate bound in a binder formed from sialon, thesematerials being used for the manufacture of plates and nozzles ofslide-valve shut-off devices for steel-making ladles and tundishes.

The lifetime of these components very rapidly decreases when they areexposed to very corrosive steels, such as ultra-low-carbon steelstreated with calcium carbide (CaSi), that is to say those containing ahigh dissolved calcium content (>50 ppm).

Finally, materials are known from EP-A-0,482,981 and EP-A-0,482,984which are based on various refractory granulates, respectively bound inan aluminium nitride or sialon matrix and containing dispersed materialsof graphite and/or of boron nitride. These materials are useful formanufacturing slide-valve plates, but above all for manufacturingfeed-stream shroud tubes, submerged nozzles and stopper rods. Theadditions of BN and graphite make it possible to achieve the excellentheat shock resistance required by these applications. However, thesematerials are attacked, in their binding matrix, when they are used forlong periods in contact with corrosive steel.

Common to the prior-art materials mentioned is a nitrided bindingmatrix, obtained by the in situ reactive sintering under nitrogen eitherof aluminium or of a mixture of aluminium, alumina and silica. Thesematerials therefore have all the characteristics specific to bindingmatrices obtained by the reactive sintering of metal powder undernitrogen, namely excellent hot strength, low open porosity and, aboveall, small-diameter pores, guaranteeing low wettability and goodresistance to infiltration by molten metals and slag.

The present invention aims to provide novel refractory materials andcomponents based on the same granulates, whose general characteristicsare at least equivalent to those of the prior materials and components,in particular the low porosity and the high hot strength, but whoseresistance to matrix corrosion by steels is significantly improved, aswell as a process for manufacturing these materials.

More particularly, the invention relates to novel refractory materialscharacterized in that they comprise, in % by weight:

A! 32 to 87% of particles and/or grains of at least one refractorymaterial the melting temperature and thermal dissociation temperature ofwhich are greater than 1700° C., this material being chosen fromcorundums, mullite, materials of the alumina-zirconia system, magnesia,pure or partially stabilized zirconias, on condition that their particlesize is at least 50 μm, the MgO-Al₂ O₃ spinel, whether these productsare electrically fused or sintered, the electrically fused materialshaving an alumina content of at least 85% by weight and the electricallyfused materials of the alumina-silica-zirconia system containing atleast 40% of alumina and 5% of zirconia, aluminium oxycarbides of theAl₄ O₄ C and Al₂ OC types, products based on aluminium oxynitride,bauxite, and refractory argillaceous chamottes;

B! 7 to 50% of an in situ-formed binding matrix consisting mostly:

either of a sialon of formula Si_(6-z) Al_(z) O_(z) N_(8-z) where zequals 0 to 4, as determined from an X-ray diffraction pattern;

or of aluminium nitride AIN of hexagonal structure and/or of at leastone of the AIN polytypes, denoted in the Ramsdell notation by 2H, 8H,27R, 21R, 12H and 15R, as determined from an X-ray diffraction pattern;

or of a mixture of these constituents;

C! 2 to 40% of a material based on titanium nitride TiN dispersed in thematrix; and, optionally,

D! 0 to 42% of hexagonal boron nitride, amorphous carbon, and/orcrystallized graphite dispersed in the binding matrix.

The invention also relates to refractory components which are to beexposed to contact with a molten metal, characterized in that theyconsist of a refractory material comprising, in % by weight:

A! 32 to 87% of particles and/or grains of at least one refractorymaterial, the melting temperature and thermal dissociation temperatureof which are greater than 1700° C.;

B! 7 to 50% of an in situ-formed binding matrix consisting mostly:

either of a sialon of formula Si_(6-z) Al_(z) O_(z) N_(8-z) where zequals 0 to 4, as determined from an X-ray diffraction pattern;

or of aluminium nitride AIN of hexagonal structure and/or of at leastone of the AIN polytypes, denoted in the Ramsdell notation by 2H, 8H,27R, 21R, 12H and 15R, as determined from an X-ray diffraction pattern;

or of a mixture of these constituents;

C! 2 to 40% of a material based on titanium nitride TiN dispersed in thematrix; and, optionally,

D! 0 to 42% of hexagonal boron nitride, amorphous carbon, and/orcrystallized graphite dispersed in the binding matrix.

As examples of refractory materials which can constitute the grains orparticles A!, mention may be made, in a non-limiting way, of corundums,mullite, materials of the alumina-zirconia system, magnesia, pure orpartially stabilized zirconias, on condition that their particle size isat least 50 μm, the MgO-Al₂ O₃ spinel, whether these products areelectrically fused or sintered, the electrically fused materials havingan alumina content of at least 85% by weight and the electrically fusedmaterials of the alumina-silica-zirconia system containing at least 40%of alumina and 5% of zirconia, aluminium oxycarbides of the Al₄ O₄ C andAl₂ OC types, products based on aluminium oxynitride, bauxite, andrefractory argillaceous chamottes and silicon carbide. The choice of thenature of the grains or particles used will depend on the particularapplication envisaged; they contribute specifically to the corrosionresistance, the erosion resistance and the abrasion resistance of thematerial, as well as to its thermal conductivity. They are essentiallyemployed in order to lower the manufacturing cost of the products.

The proportion of grains or particles A! in the materials and componentsof the invention may vary widely depending on the properties of thematerial desired. The proportion of A! may range from approximately 32to 87% by weight. Currently a proportion of from approximately 36 to 68%by weight is preferred. The granulate A! content is usually defined soas to bring the composition up to 100% after the B!, C! and D! contentshave been fixed.

The particle size of constituent A! (also called "granulate") may varywidely depending on the nature of the said constituent and the desiredproperties of the final material or component. The size of the particlesor grains of constituent A! may vary widely, this lying within the rangeof from 1 μm to 10 mm. Particles smaller than 1 μm are not advantageousas they are too difficult to manufacture or are likely to haveundesirable or excessive reactivity. Grains larger than 10 mm are not atall desirable as they give the material a poor appearance and they arenot suitable for manufacturing thin components.

The binding phase B!, which binds the grains A! together, consistsmostly of sialon of formula Si_(6-z) Al_(z) O_(z) N_(8-z), where zequals from 0 to 4 and preferably from 2.5 to 3.5, or of aluminiumnitride AIN or of a polytype of aluminium nitride or of a mixture ofthese constituents.

The proportion of the binding phase B! itself may also vary widely. Theproportion of binding phase B! may range from approximately 7 to 50% byweight. The lower band is so-defined because of the need for thematerial to maintain good properties in terms of porosity and strengthand the upper band because of economic reasons which would indicate asmuch of constituents A! as possible.

Usually the proportion of binder B! is chosen depending on the type ofthe constituent A! used.

Broadly speaking, three main types of materials may be distinguished:

materials having a coarse granulate A!, that is to say those for whichconstituent A! is formed from at least 90% by weight of grains having adiameter lying between 50 μm and 10 mm. These coarse-granulate materialsadvantageously contain a relatively low proportion of binder B!, forexample from 7 to 18% by weight, preferably from 12 to 18%, and arerelatively low-cost materials having acceptable porosity and strengthproperties;

materials having a fine granulate A!, that is to say those for whichconstituent A! is formed from at least 90% by weight of particles havinga diameter less than 50 μm. These fine-granulate materialsadvantageously contain a relatively high proportion of binder B!, forexample from 30 to 50% by weight, preferably from 30 to 45%, and arematerials with excellent mechanical characteristics (very high coldflexural strength) and very good tribological properties due to the highbinder content (low coefficient of friction, low degree of abrasion withrespect to other ceramics and to metals). In addition, they allowcomponents with very small tolerances to be produced. On the other hand,their manufacturing cost is substantially higher than that ofcoarse-granulate materials;

materials having a mixed granulate A!, that is to say a granulate formedby a mixture of relatively coarse and relatively fine particles, whichhave intermediate properties. These materials usually contain an averageproportion of binder B!, for example from 15 to 35% by weight.

The binder contents of the abovementioned main types are only given byway of indication and various factors, such as the corrosion resistanceor the heat shock resistance specific to the granulate selected, maycome into play and lead to compositions lying outside the ranges ofproportions recommended for each type.

Constituent C! may be any material based on titanium nitride. Forexample, this may be a titanium nitride powder of greater than 99%purity, or a powder of a TiN-TiC solids solution containing at most 30%of TiC, this having the advantage of resulting in good performancecharacteristics while being less expensive to produce than pure TiN.

The proportion of constituent C! may vary from 2 to 40%, preferably from2 to 20%. Currently, it is most particularly preferred to incorporatefrom 5 to 15% of C!. Preferably, at least 90% of the particles ofconstituent C! are between 1 and 100 μm.

Ingredient D!, optionally dispersed in the binding phase, may consist ofboron nitride, amorphous carbon, crystallized graphite or a mixturethereof. The crystallized graphite is preferably in the form of flakes.Ingredient D! may contribute to improving the heat shock nature of thematerials or components and to improving their property of not beingwetted by metals and slag, as well as their tribological properties.

The proportion of particles D! may also vary widely. The proportion ofparticles D! may range from 0 to 42% by weight. Currently, a proportionof from approximately 5 to 30% is preferred.

The invention also relates to a process for manufacturing refractorymaterials according to the invention.

This process is characterized in that:

1. An initial charge is prepared which comprises a mixture of thefollowing constituents in the proportions indicated:

a) 32 to 90% by weight, preferably from 40 to 75%, of grains and/orparticles consisting of a refractory material whose melting temperatureand possible thermal dissociation temperature are greater than 1700° C.;

b) 6 to 42% by weight of a mixture of reactive powders, essentiallyconsisting of:

1. In the case of a sialon matrix

(i) 23 to 90%, preferably from 25 to 45%, of silicon powder, at least90% of the particles of which have a diameter less than 150 μm,

(ii) 0 to 62%, preferably from 30 to 55%, of calcined alumina, at least90% of the particles of which have a diameter of less than 20 μm,

(iii) 0 to 28%, preferably from 11 to 25%, of aluminium powder, at least90% of the particles of which have a diameter less than 80 μm, the totalof constituents (i) to (iii) representing 100% and the ratio of theproportion of aluminium to the proportion of calcined alumina being lessthan 0.7.

2. In the case of a binding matrix of aluminium nitride

100% of aluminium powder, at least 90% of the particles of which have adiameter less than 80 μm.

3. In the case of a binding matrix consisting of one of the polytypes ofaluminium nitride

85 to 25% by weight of silicon and aluminium powders in a maximum Sipowder/Al powder ratio of 0.8, these powders being combined withcalcined alumina in a proportion of from 15 to 75% by weight.Preferably, a mixture is used which comprises, by weight:

(i) 10 to 20% of silicon powder, at least 90% of the particles of whichhave a diameter less than 150 μm;

(ii) 25 to 65% of calcined alumina powder, at least 90% of the particlesof which have a diameter less than 20 μm;

(iii) 25 to 60% of aluminium powder, at least 90% of the particles ofwhich have a diameter less than 80 μm, the total of constituents (i) to(iii) representing 100%;

c) 2 to 43% of powder of a material based on titanium nitride, at least90% of the particles of which preferably have a diameter lying between 1and 100μm;

d) 0 to 44% by weight, preferably 5 to 33%, of particles of hexagonalboron nitride, amorphous carbon particles, crystallized graphiteparticles or a mixture of these;

e) 0 to 3% of a dried and ground refractory clay, the total ofingredients (a) to (e) making 100%; and

f) a small amount of temporary binder;

2. the resulting mixture is given the desired shape by pressing;

3. the so-shaped mixture is dried; and

4. the so-shaped mixture is fired and dried in a nitrogen-basedatmosphere at a temperature of from 1300° C. to 1600° C.

In order to obtain the preferred binding matrix of sialon having theindicated formula in which z=2.5 to 3.5, it has been found that it isnecessary to use a mixture of reactive powders comprising, by weight,(i) 25-45% of the silicon powder, (ii) 30-55% of the calcined aluminaand (iii) 11-25% of the aluminium powder.

The shaping carried out in step 2 may be carried out in a conventionalmanner by uniaxial or isostatic pressing. The role of the clay (e) isthat of a pressing additive which facilitates the shaping operation.

The drying step 3 may be carried out at a moderately high temperature,for example from 100 to 200° C., preferably at about 150° C.

The duration of the firing step 4 may vary widely depending on the sizeof the article shaped and dried. By way of indication, the temperaturehold of from 4 to 10 hours at a temperature of approximately 1300-1600°C. is usually satisfactory. The expression "nitrogen-based atmosphere"means an atmosphere of which the main constituent is nitrogen. Such anatmosphere may contain other gases in minor proportions, such as inertgases (for example argon), hydrogen or carbon monoxide.

It should be noted that there is a difference between the granulate,titanium nitride, graphite and boron nitride contents of the initialmixture and the proportion of the same constituents in the finalproduct, since the firing is accompanied by nitrogen fixation andtherefore by an increase in weight.

The grains and/or particles (a) may have a size lying within the rangeof from 1 μm to 10 mm, as indicated above for constituent A!. The grainsand/or particles (a) may be chosen from the materials definedhereinabove for constituent A!. However, with regard to particles (a)having a size of less than 50 μm, the use of pure or stabilizedzirconium should be avoided since, in this finely divided form and underthe firing conditions, zirconium can react with nitrogen to form ZrNwhich, in service, oxidizes easily and may cause the material to fail.

The grains and/or particles (a) may consist of just one type ofrefractory material or of a mixture of refractory materials. Inparticular, it is possible to use a mixture of grains (>50 μm) of arefractory material and of particles (<50 μm) of another refractorymaterial, in respective proportions of 32-90% and 1-25% by weight.

Currently, it is preferred for the grains and/or particles (a) tocontain at least a small amount (>1% by weight) of alumina having aparticle size less than 50 μm when the binding matrix B! is aluminiumnitride or a polytype of aluminium nitride.

The mixture (b) of reactive powders represents 6-42% by weight of theinitial charge. Preferably, 25-38% by weight of mixture (b) is used forpreparing a fine-granulate material and 10-15% by weight of the saidmixture (b) for preparing a coarse-granulate material.

In the mixture (b), the calcined alumina particles (ii) are particles ofreactive alumina which react with the ingredients (i) and (iii) duringthe step of firing under nitrogen, in order to form the sialon phase ora AIN polytype.

The titanium-nitride-based constituent (c) is preferably substantiallypure titanium nitride, but it may also be sufficient to use a powder ofa TiN-TiC solid solution containing up to approximately 30% by weight ofTiC.

The ingredient (d) may consist of particles of hexagonal BN or ofamorphous carbon (for example carbon black) or of graphite particles.These particles may be fine or coarse. The addition of relatively coarseparticles or flakes (>40 μm and preferably >100 mm) of graphite isadvantageous when it is desired to improve the heat shock resistance ofthe final material. In contrast, the addition of carbon black (fineparticles of C) is advantageous when it is desired to improve thecorrosion resistance of the final material.

The temporary binder (f) may consist of any known temporary binder. Byway of example, mention may be made of phenolic resins, furfurylalcohols and polyvinyls, aqueous solutions of dextrin or ofcarboxymethyl cellulose, or of calcium lignosulphonate. By way ofindication, an amount of temporary binder of the order of fromapproximately 1 to 4% by weight with respect to the total of ingredients(a) to (e), has usually proved to be satisfactory in order to ensurethat the material has good green properties without appreciabledeterioration of its general properties.

The invention is illustrated, in a non-limiting way, by the followingexamples. In these examples, 220×110×60 mm test bricks were preparedusing a procedure in which the initial constituents were mixed, per 10kg charge, in a Bonnet mixer, shaped into bricks using a hydraulic pressexerting a pressure of 1000 bar, dried at 150° C. and then fired undernitrogen, in an industrial electric furnace, at a temperature of from1300 to 1600° C. for 4 to 10 hours, depending on the case.

The properties of the materials were determined using the followingtests:

Hot flexural strength: measured in air, after accelerated heating inorder to limit the effects of oxidation (measurements carried out underargon generally lead to much higher values, but this test is veryexpensive).

Heat shock resistance: we have expressed this by the loss (in percent,of cold flexural strength measured on 125×25×25 mm bars after thefollowing treatment:

Suddenly putting the room-temperature test specimens into an oven heatedto 120° C., holding them there for 30 min and then quenching the testspecimens in cold water.

Resistance to corrosion by steel, cast iron and special alloys:

It is measured using the so-called self-crucible method: the crucibleconsists of a block of the refractory to be studied, having a 110×110×60mm format. A 24 mm diameter and 40 mm deep hole is drilled into one ofthe large faces using a diamond drill. A fixed amount of steel (from 30to 40 g) is put into the crucible thus formed. The crucible is coveredwith a 110×110×10 mm cover, made of the same material, and then placedin an electric furnace where it is heated in air to a definedtemperature and for a defined time.

After cooling, the crucible is sawn vertically in a plane of symmetryand damage to the refractory is observed at the metal/refractoryinterface. The corroded thickness, with respect to the initial diameter,is also measured.

This test, which is highly corrosive since it is carried out underoxidizing conditions, has however only a relative value. This is why, ineach firing, a crucible of a reference product of known in-servicebehaviour is included. The degree of corrosion is then expressed in theform of an index which is equal to 100 times the wear in mm of thecrucible formed by the product being studied divided by the wear in mmof the reference product.

In the examples mentioned hereinbelow, the test conditions were asfollows:

Steel: XC38;

Temperature: 1600° C.;

Temperature hold time: 3 h.

In the examples, the following raw materials were used:

Silicon carbide sold by the Pechiney Electrometallurgie company, underthe name Arbina Cristallise. This is a material essentially consistingof the alpha SiC variety and containing on average 98.5% of SiC bychemical analysis.

Electrically fused black corundum corresponding to the followinganalysis in % by weight: Al₂ O₃ =96%, TiO₂ =3%, SiO₂ =0.6%, Fe₂ O₃=0.2%, CaO+MgO+Na₂ O+K₂ O=0.2%.

Commercial calcined fine alumina containing at least 99.5% of Al₂ O₃,having an average particle size of approximately 5 μm with 90% of theparticles lying between 1 and 20 μm.

Tabular alumina sold by the ALCOA company under the name "TabularAlumina T 60", 95% of the particles of which are smaller than 45 μm. Thetabular alumina is a calcined alumina, sintered at high temperature andground.

Commercial powdered silicon, sold under the name "T140 Silicon" by thePechiney Electrometallurgie company, at least 90% of the particles ofwhich have a size less than 150 μm.

Commercial powdered aluminium, sold under the name "Aluminium 200 TV" bythe Pechiney Electrometallurgie company, at least 90% of the particlesof which have a size less than 80 μm.

Natural graphite crystallized in the form of flakes, originating fromChina or Madagascar, having an ash content of less than 17% by weightand at least 80% of the particles of which have a size greater than 100μm.

Hexagonal boron nitride, sold under the name HCST-AO5 by the Herman C.Starck company. This nitride is formed by agglomerates having a size offrom 1 to 10 mm, consisting of individual laminae having a size of fromapproximately 0.5 to 1 μm.

Ground clay, sold under the name "DA.40/42" by the Denain Anzin Minerauxcompany, corresponding to the following chemical analysis, in % byweight: Al₂ O₃ =36%, SiO₂ =47%, Fe₂ O₃ =1.8%, TiO₂ =1.8%, CaO+MgO+Na₂O+K₂ O=0.8%, loss on ashing: 12.6%.

Titanium nitride, of T1153 quality, marketed by the CERAC company, thispowder containing 99.5% of TiN and the maximum diameter of the grainsbeing less than 50 μm.

Spinel: an electrically fused MgO-Al₂ O₃ spinel assaying at 69% Al₂ O₃and 30% MgO, marketed by the Pechiney company;

sintered magnesia: a magnesia sold under the name Nedmag 99 by theBilliton Refractories company and corresponding to the followingspecifications: MgO>98%, SiO₂ <1%, B₂ O₃ <0.05%, with a CaO/SiO₂ratio>2;

Alumina-zirconia: an Al₂ O₃ -ZrO₂ fused granular material assaying at39% ZrO₂ and 60% Al₂ O₃ sold by the Norton company under the name NzAlundum.

The following non-limiting examples are given for the purpose ofillustrating the invention.

EXAMPLE 1

Using the general operating method described hereinabove, 6 specimens Ato F formed by grains of corundum with a sialon-TiN binder wereprepared, these mixtures differing from each other by the proportion ofTiN in the initial charge, as well as in the final product.

Table 1 recapitulates the constituents of the initial charge and theirproportions in % by weight and various properties of the materialsobtained, with respect to those of the reference composition R1 outsidethe invention.

It may be seen that the additions of TiN rapidly improve the resistanceof the material to corrosion by steel. Above 20% of TiN, however, adegradation of the behaviour in the corrosion test can be observed. Thisdegradation results essentially from the oxidizing character of saidtest. Additions greater than 20% of TiN are nevertheless interesting forapplications in low oxidizing conditions (refer to Example 8).

The hot strength at 1500° C. is maintained at a high level up to 30% ofTiN.

EXAMPLE 2

The mixtures R2 and R3, formed by grains of corundum, metal powdersintended for the synthesis of the sialon and metallic titanium powderintended for the in situ synthesis of TiN. These examples are outsidethe invention.

In these tests, the metallic titanium powder had the T1146 quality ofgreater than 99.5% purity and at least 90% of the particles of whichhave a diameter of less than 75 μm, this powder being supplied by theCERAC company.

Table 2 recapitulates the constituents of the initial charge and theirproportions in % by weight, with respect to composition C which comeswithin the scope of the invention.

These specimens were prepared using the operating method describedhereinabove.

After firing, the specimens R2 and R3 had completely disintegrated.

This test shows that the in situ formation of TiN from metallic titaniumpowder, whether or not combined with aluminium or silicon metallicpowders, is not suitable for producing the refractory materialsconcerned in the invention.

Production of a compact, low-porosity and mechanically strong bindingmatrix therefore requires the dispersion of presynthesized titaniumnitride powder in an aluminium and/or silicon powder mixture, whichpowders produce the desired reactive sintering under nitrogen.

EXAMPLE 3

Using the operating method described hereinabove, two specimens G and H,formed by corundum grains were prepared, the binding matrix of whichcontains titanium nitride and, respectively, AIN and AIN15R. Table 3recapitulates the constituents of the initial charge, their proportionsand various properties of the materials obtained. Specimen C recalls thecharacteristics of a product having a sialon-TiN binding matrix.

It is apparent that the invention also applies to the AIN and AIN15Rreactive binders. These make it possible to increase the flexuralstrength of the materials appreciably, as well as the resistance tocorrosion by steel compared to sialon. However, they are more sensitiveto heat shock.

EXAMPLE 4

Using the operating method described hereinabove, 7 specimens referencedB and I to N, formed by corundum grains having a sialon-TiN binder wereprepared from an initial charge containing respectively variousproportions of graphite flakes.

Table 4 recapitulates the constituents of the initial charge and theirproportions in % by weight and various properties of the materialsobtained. The specimen R4, given by way of indication, is outside thescope of the invention. It was prepared according to EP-A-0,482,984 andcorresponds to a material commonly used today for submerged nozzles.

An appreciable improvement in the heat shock resistance is observed fora graphite content (measured in the final product) greater than 4%.

For the very high graphite content (specimen M), the heat shockresistance is close to that of the alumina-graphite product having asialon binder R4 of the same graphite content. A spectacular improvementin the resistance to corrosion by steel is observed by the addition of5% of TiN.

EXAMPLE 5

Using the operating method described hereinabove, the specimen O, formedby corundum grains having a AIN binder containing 8% of boron nitrideand 3% of TiN was prepared. Table 5 recapitulates the constituents ofthe initial charge, their proportions and various properties of thematerial obtained. Specimen R5, mentioned by way of comparison, isoutside the scope of the invention.

An appreciable improvement in the resistance to corrosion by steel isobserved for a small addition of TiN.

It may also be observed that the hot strength is maintained up to a highlevel and that the heat shock resistance is not affected.

EXAMPLE 6

According to the operating method described hereinabove, 4 specimens,formed by various types of grains bound in a binding matrix of sialoncontaining 8.3% of titanium nitride dispersed within the binding matrixwere prepared.

Table 6 summarizes the constituents of the initial charge as well astheir proportions and gives the properties of the materials obtained.

The excellent physical properties obtained show that the inventionapplies to most of the usual refractory granulates.

The basic granulates, of the spinel or magnesia type, are preferred forapplications in which corrosion by a basic slag or a cover powder is thepredominant stress, or else in the case of special alloys.

The alumina-zirconia granulate is preferred for applications in whichheat shock is predominant, such as, for example, in the case ofslide-valve shut-off plates.

The SiC granulate is more particularly be used in blast furnaces inwhich excellent abrasion resistance and high thermal conductivity aredesired.

EXAMPLE 7

Using the general operating method described hereinabove, a specimen T,formed by particles of fine tabular alumina (<45 μm), boron nitride,graphite and a sialon-TiN binder, was prepared.

Table 7 recapitulates the constituents of the initial charge and theirproportions in weight % and various properties with respect to those ofthe reference composition R6, outside the invention.

Comparison of the characteristics of T and R6 shows the advantage ofadding titanium nitride to the compositions having a fine structure anda high binder content in order to improve their resistance to corrosionby steel.

EXAMPLE 8

Using the general operating method described hereinabove, specimens U toX according to the invention and two specimens R7 and R8 outside theinvention were prepared, varying the proportion of TiN. For thecorrosion test, crucibles, as described above, have been embedded withina refractory concrete in order to reduce the oxidizing character of thetest.

Table 8 recapitulates the constituents of the initial charge and theirproportion in % by weight, the properties of the resulting materials andthe mineralogical composition of the latter.

It can be seen that, in these less oxidizing conditions, even smalladditions of TiN improve the resistance to corrosion by steel. On thecontrary, an excessive addition (higher than 40%) causes a degradationof the resistance to corrosion by steel as well as of the open porosity.

                                      TABLE 1    __________________________________________________________________________                         R1 A  B  C  D  E  F    __________________________________________________________________________    Composition           Black corundum, 2-0.2 mm                         50 50 50 50 50 50 50           Black corundum, 0.2-0.05 mm                         35.2                            35.2                               32.1                                  29 24.8                                        16.5                                           6.2           Calcined fine alumina                         6.1                            4  4  4  4  4  4           Aluminium, 200 TV                         2.2                            2.2                               2.2                                  2.2                                     2.2                                        2.2                                           2.2           Silicon, T140 4.5                            4.5                               4.5                                  4.5                                     4.5                                        4.5                                           4.5           Titanium nitride                         0  2.1                               5.2                                  8.3                                     12.5                                        20.8                                           31.1           Clay, DA 40/42                         2  2  2  2  2  2  2           CMC solution  +3.2                            +3.2                               +3.2                                  +3.2                                     +3.2                                        +3.2                                           +3.2    Properties           Density after nitride formation                         3.24                            3.30                               3.29                                  3.38                                     3.31                                        3.32                                           3.27           Open porosity (%)                         14.6                            13.5                               13.9                                  11.7                                     13.3                                        15.4                                           19           Flexural strength (MPa)           at 20° C.                         19.2                            21.6                               21.6                                  27.7                                     22 29.3                                           21.3           at 1500° C                         17.5                            17.4                               14.3                                  17.5                                     13.5                                        11.5                                           13           Heat shock resistance: loss of FS                         -67                            -64                               -63                                  -66                                     -61                                        -69                                           -61           after quenching (%)    Mineralogical           TiN (%)       0  2  5  8  12 20 30    composition           Sialon (%)    14.5                            14.5                               14.5                                  14.5                                     14.5                                        14.5                                           14.5    Steel corrosion index                         100                            100                               68 50 59 120                                           220    __________________________________________________________________________

                  TABLE 2    ______________________________________                R2        R3     C    ______________________________________    Black corundum,                  50          50     50    2-0.2 mm    Black corundum,                  19.5        23.8   29    0.2-0.05 mm    Calcined fine alumina                  7           4      4    Aluminium, 200 TV                  0           7.3    2.2    Silicon, T140 0           5.3    4.5    Metal Ti powder                  20.5        6.6    0    Titanium nitride                  0           0      8.3    Clay, DA 40/42                  3           3      2    CMC solution  +3.7        +3.7   +3.2    Density after nitride                  Products not viable                                 3.38    formation    Flexural strength at                  Disintegration during                                 27.7    20° C. (MPa)                  firing    ______________________________________

                  TABLE 3    ______________________________________                       C     G      H    ______________________________________    Composition            Nature of the reactive binder                             Sialon  AIN  AIN 15R    type    Black corundum, 2-0.2 mm                             50      50   50            Black corundum,  29      26.5 22.5            0.2-0.05 mm            Calcined fine alumina                             4       --   9            Aluminium, 200 TV                             2.2     12   5            Silicon, T140    4.5     --   2            Titanium nitride 8.3     8.5  8.5            Clay, DA 40/42   2       3    3            CMC solution     +3.2    +3.2 +3.2    Properties            Density after nitride formation                             3.30    3.24 3.23            Flexural strength at 20° C.                             27.7    43.3 35            (MPa)            Flexural strength at 1500° C.                             17.5    26   21            (MPa)            Heat shock resistance (%)                             -66     -85  -80    Mineral-            TiN (%)          8       8    8    ogical  Sialon (%)       14.5    0    traces    composition            AIN (%)          0       17   0            AIN15R (%)       0       traces                                          20    Steel corrosion index                         50      16     46    ______________________________________

                                      TABLE 4    __________________________________________________________________________                   B  I  J  K  L  M  N  R4    __________________________________________________________________________    Black corundum, 2-0.2 mm                   50 50 50 50 45 40 25 40    Black corundum, 0.2-0.05 mm                   32.1                      23.8                         19.8                            15.8                               12.8                                  7.8                                     7.8                                        8    Calcined fine alumina                   4  5.8                         5.8                            5.8                               5.8                                  5.8                                     5.8                                        10.8    Aluminium, 200 TV                   2.2                      3.2                         3.2                            3.2                               3.2                                  3.2                                     3.2                                        3.2    Silicon, T140  4.5                      6  6  6  6  6  6  6    Titanium nitride                   5.2                      5.2                         5.2                            5.2                               5.2                                  5.2                                     5.2                                        0    Flaked graphite                   0  4  8  12 20 30 45 30    Clay, DA 40/42 2  2  2  2  2  2  2  2    CMC solution   +3.2                      +3.0                         +2.8                            +2.8                               +2.8                                  +2.8                                     +2.8                                        +2.8    Density after nitride formation                   3.29                      31.9                         3.14                            3.10                               2.98                                  2.57                                     2.50                                        2.55    Flexural strength at 20° C. (MPa)                   21.6                      20 19 17 15 9  8  8.9    Heat shock resistance                   -63                      -60                         -55                            -48                               -39                                  -32                                     -15                                        -36    TiN (%)        5  5  5  5  5  5  5  0    Sialon (%)     14.5                      14.5                         14 14 13.8                                  14.3                                     14.4                                        14.5    Graphite (%)   0  4  7.8                            11.3                               18.2                                  27 40 27    Steel corrosion index                   68 69 60 48 36 22 23 90    __________________________________________________________________________

                  TABLE 5    ______________________________________                           R5   O    ______________________________________    Composition Black corundum,  50     50                2-0.2 mm                Black corundum, 0.2-0.05                                 26.5   26.5                mm                Aluminium, 200 TV                                 12     9                TiN (%)          0      3                BN (%)           8.5    8.5                Clay, DA 40/42   3      3                CMC solution     +3.2   +3.2    Physical cha-                Density after nitride                                 3.11   3.16    racteristics                formation                Flexural strength at                                 23     23.6                1500° C. (MPa)                Heat shock resistance                                 -61    -62    Mineralogical                AIN (%)          17     13    components  TiN (%)          0      3                BN (%)           8      8    Steel corrosion index    90     70    ______________________________________

                                      TABLE 6    __________________________________________________________________________    Specimen        C    P     Q    R    S    __________________________________________________________________________    Grain type      Black                         MgO/Al.sub.2 O.sub.3                               Sintered                                    Alumina-                                         SiC    (2 mm to 0.05 mm) %                    corundum                         spinel                               magnesia                                    zirconia                                         75                    79   79    75   79    Calcined fine alumina                    4    4     8    4    8    Silica, T140    4.5  4.5   4.5  4.5  4.5    Aluminium, 200 TV                    2.2  2.2   2.2  2.2  2.2    Titanium nitride                    8.3  8.3   8.3  8.3  8.3    Clay, DA 40/42  2    2     2    2    2    CMC solution    +3.2 +3.2  +3.2 +3.2 +3.0    Apparent density                    3.38 3.12  3.09 3.42 2.86    Open porosity % 11.7 12.1  15.3 12.4 12.8    Flexural strength at 20° C. (MPa)                    27.7 25    22   26.3 45    Flexural strength at 1500° C. (MPa)                    17.5 12.2  9.8  24.6 40    Heat shock resistance (%)                    -66  -70   -72  -50  -75    __________________________________________________________________________

                  TABLE 7    ______________________________________                        R6      T    ______________________________________    Tabular alumina - 325 mesh                          48        35.5    Calcined fine alumina 14.3      14.3    Silicon, T140         16        16    Aluminium, 200 TV     7.7       7.7    Titanium nitride      0         12.5    Boron nitride         6         6    Flaked graphite       6         6    Clay, DA 40/42        2         2    CMC solution          +3.0      +3.4    Density after nitride 2.80      2.85    formation    Flexural strength at 20° C. (MPa)                          50        53    Steel corrosion index 100       80    ______________________________________

                                      TABLE 8    __________________________________________________________________________                      R7  U   G   V   W   X   R8    __________________________________________________________________________    Composition           Black corundum, 2-0.2                      50  50  50  50  50  42.5                                              31.9           mm           Black corundum, 0.2-                      35  31.8                              26.5                                  19.1                                      8.4 0   0           0.05 mm           Aluminium, 200 TV                      12  12  12  12  12  12  12           Titanium nitride                      0   3.2 8.5 15.9                                      26.6                                          42.5                                              53.1           Clay, DA 40/42                      3   3   3   3   3   3   3           CMC solution                      +3.2                          +3.2                              +3.2                                  +3.2                                      +3.2                                          +3.2                                              +3.2    Properties           Density after nitride                      3.13                          3.19                              3.24                                  3.24                                      3.16                                          3.17                                              3.20           formation           Open porosity (%)                      15.4                          13.9                              12.6                                  11.6                                      14  15  18           Flexural strength at                      49.4                          44.2                              43.3                                  40.2                                      32  30  20           20° C. (MPa)           Heat shock resistance,                      -92 -88 -85 -80 -78 -75 -68           loss of FS after quench-           ing (%)    Mineralogi-           TiN (%)    0   3   8   15  25  40  50    cal composition           AIN (%)    17  17  17  17  17  17  17           AIN 15R (%)                      Traces                          Traces                              Traces                                  Traces                                      Traces                                          Traces                                              Traces    Steel corrosion index                      100 47  21  80  87  93  120    __________________________________________________________________________

We claim:
 1. A refractory material which comprises, in % by weight:A) 32to 87% of particles and/or grains of at least one refractory materialhaving a melting temperature and a thermal dissociation temperaturegreater than 1700° C., selected from groups 1-4, 1) a material selectedfrom the group consisting of electrically fused or sintered corundums,mullite, alumina-zirconia system materials, magnesia, MgO-Al₂ O₃ spinel,and pure or partially stabilized zirconias having a particle size of atleast 50 μm; 2) electrically fused materials having an alumina contentof at least 85% by weight and electrically fused alumina-silica-zirconiasystem materials containing at least 40% of alumina and 5% of zirconia;3) aluminum oxycarbides of the formula Al₄ O₄ C and Al₂ OC, aluminumoxynitride-based materials, bauxite, and 4) refractory argillaceouschamottes; B) 7 to 50% of an in situ-formed binding matrix consistingessentially of: either (i) a sialon of formula Si_(6-z) Al_(z) O_(z)N_(8-z) where z is an amount greater than 0 to 4, as determined from anX-ray diffraction pattern; or (ii) aluminum nitride AlN of hexagonalstructure and/or of at least one of the AlN polytypes, denoted in theRamsdell notation by 2H, 8H, 27R, 21R, 12H and 15R, as determined froman X-ray diffraction pattern; or of a mixture of (i) and (ii); C) 2 to40% of titanium nitride dispersed in the matrix; and D) 0 to 42% of atleast one of hexagonal boron nitride, amorphous carbon and crystallizedgraphite dispersed in the binding matrix.
 2. A refractory materialaccording to claim 1, wherein A) comprises 36 to 68% of the weight ofthe material.
 3. A refractory material according to claim 1, whereinconstituent A) has a particle size of between 1 μm and 10 mm.
 4. Arefractory material according to claim 1, wherein constituent C)comprises from 5 to 15% of the weight of the material.
 5. A refractorymaterial according to claim 1, wherein constituent A) is formed in aproportion of at least 90% by weight by grains having a diameter between50 μm and 10 mm, and which contains from 12 to 18% of binding matrix B).6. A refractory material according to claim 1, wherein constituent A) isat least 90% by weight by particles having a diameter less than 50 μm,and which contains from 30 to 45% of binder B).
 7. A refractory materialaccording to claim 1, which contains from 5 to 30% by weight ofconstituent D).
 8. A process for manufacturing a refractory material,comprising:preparing an initial charge comprised of a mixture of thefollowing constituents in the proportions indicated:a) 32 to 90% byweight of grains and/or particles consisting of a refractory materialhave a melting temperature and possible thermal dissociation temperaturegreater than 1700° C.; b) 6 to 42% by weight of a mixture of reactivepowders, consisting essentially of either:a sialon matrix formingmixture of(i) 23 to 90% of silicon powder, at least 90% of particles ofwhich have a diameter less than 150 μm, (ii) 0 to 62% of calcinedalumina, at least 90% of the particles of which have a diameter of lessthan 20 μm, (iii) 11 to 28% of aluminum powder, at least 90% of theparticles of which have a diameter less than 80 μm, the total ofconstituents (ii) to (iii) representing 10% and the total of theconstituents (i) to (iii) representing 100% and the ratio of theproportion of aluminum to the proportion of calcined alumina being lessthan 0.7; or an aluminum nitride matrix precursor consisting of 100% ofaluminum powder, at least 90% of the particles of which have a diameterless than 80 μm; or aluminum nitride polytype forming mixture of 85 to25% by weight of silicon and aluminum powders in a maximum Si powder/Alpowder ratio of 0.8, said powders being combined with calcined aluminain a proportion from 15 to 75% by weight; c) 2 to 4.3% of powder of atitanium nitride-based materials; d) 0 to 44% by weight of particles ofat least one of hexagonal boron nitride, amorphous carbon particles andcrystallized graphite particles; and e) 0 to 3% of a dried and groundrefractory clay, the total of ingredients a) to e) making 100%; pressingthe mixture to a shape; drying the resultant shaped mixture; and firingand drying said shaped mixture in a nitrogen-based atmosphere at atemperature of from 1300° C. to 1600° C.
 9. The process according toclaim 8, wherein ingredient a) represents 40-75%; ingredient b)represents 25-38% when a) is formed by particles of which at least 90%are less than 50 μm and 10-15% when a) is formed by grains of which atleast 90% are greater than 50 μm; and ingredient d) represents 5-33%.10. A refractory component which consists essentially of a refractorymaterial comprising, in % by weight:A) 32 to 87% of particles and/orgrains of at least one refractory material, the melting temperature andthermal dissociation temperature of which are greater than 1700° C.; B)7 to 50% of an in situ-formed binding matrix comprising:either 1) aSi_(6-z) Al_(z) O_(z) N_(8-z) wherein z is an amount greater than 0 to4, as determined from an X-ray diffraction pattern; or (ii) of aluminumnitride AlN of hexagonal structure and/or of at least one of AlN denotedin the Ramsdell notation by 2H, 8H, 27R, 21R, 12H and 1 SR, asdetermined from an X-ray diffraction pattern; or a mixture of (i) and(ii); C) 2 to 40% of a material based on titanium nitride dispersed inthe matrix; and D) 0 to 42% of at least one of hexagonal boron nitride,amorphous carbon, and/or crystallized graphite dispersed in the bindingmatrix.
 11. The refractory component according to claim 10, whereinconstituent A) is selected from the group consisting of electricallyfused or sintered corundums, mullite, alumina-zirconia system materials,magnesia, MgO-Al₂ O₃ spinel, and pure or partially stabilized zirconias,having a particle size of at least 50 μm; electrically fused materialshaving an alumina content of at least 85% by weight and electricallyfused alumina-silica-zirconia system materials containing at least 40%of alumina and 5% of zirconia; aluminum oxycarbides of the formula Al₄O₄ C and Al₄ O₄ C, aluminum oxynitride-based materials, bauxite,refractory argillaceous chamottes and silicon carbide.
 12. Therefractory component according to claim 10, wherein A) comprises 36 to68% of the weight of the material.
 13. The refractory componentaccording to claim 10, wherein constituent A) has a particle size ofbetween 1 μm and 10 mm.
 14. The refractory component according to claim10, wherein constituent C) constitutes from 5 to 15% of the weight ofthe material.
 15. The refractory component according to claim 10,wherein constituent A) is formed in a proportion of at least 90% byweight by grains having a diameter between 50 μm and 10 mm, and whichcontains from 12 to 18% of binding matrix B).
 16. The refractorycomponent according to claim 10, wherein constituent A) is formed in aproportion of at least 90% by weight by particles having a diameter lessthan 50 μm, and which it contains from 30 to 45% of binding matrix B).17. The refractory component according to claim 10, which contains from5 to 30% by weight of constituent D).